The present invention relates to a sorting process for sorting mail pieces and, in particular, to a sorting process wherein mail pieces sorted to an array of pockets are swept and transferred to trays for further processing.
With a growing number of mail pieces being processed, it is becoming increasingly important to provide efficient processes for sorting the mail pieces. In general, one large sorting machine is used to sort the mail for delivery to various geographic locations. Typically, the mail pieces are sorted according to a sort scheme into numerous groups (e.g. any range of ZIP codes, including 1, 3, 5, 9, 11 most significant digit sort groups, or combinations of them). The United States Postal Service gives more monetary discounts to a mailing that has a finer resolution of sortation (i.e. postal carrier route level). As such, with existing finite sized sorting machines, a large number of sort schemes and sorts will be required to properly sort the mail pieces to the resolution dictated and for carrier route qualified mail.
One known process of sorting mail utilizes a large sorting machine performing numerous sorts according to a sort scheme. A batch of mail pieces are fed into the sorting machine with the address or bar code (or both) of each mail piece being read. The sorting machine directs each mail piece into an appropriate destination xe2x80x9cpocketxe2x80x9d or xe2x80x9cbinxe2x80x9d in accordance with the sort scheme. After the entire batch is sorted with each mail piece sorted into a particular pocket, the sweeper then removes or xe2x80x9csweepsxe2x80x9d the mail pieces. During the sweeping process, all the mail pieces in the pockets are removed from the pockets. After completion of the sweeping process, a new batch of mail pieces can be sorted.
U.S. Pat. No. 5,893,464 describes a sorting process which includes the step of sorting, during a first time frame and in accordance with a first scheme, a first batch of mail pieces into a first array of pockets of the sorting machine. After the first batch of mail pieces is sorted according to the first sort scheme, the sorted mail pieces are swept from the first array of pockets of the sorting machine during a second time frame. During the second time frame, a second batch of mail pieces is sorted into a second array of pockets in accordance with a second scheme. Such a sorting system minimizes or reduces the amount of time the sorting machine is not in operation (sorting mail pieces to the pockets) and increases efficiency by minimizing the amount of time that the sorting machine is not processing mail.
However, such a system does not necessarily provide for optimum use of human workers or robotic units which must be used to sweep the pockets. Typically, four human sweepers are assigned to different zones or arrays of the sorting machine. Since some destinations will receive substantially more volume than others included in the sorting scheme or sub-scheme, one of the four sweepers may be taxed to the limit with an abundance of mail pieces, while the other three have little to do. To address this concern, one past approach has been to randomize the pocket destination code assignments so that concentrations of mail to related ZIP codes will not be clustered together with the same sweeper. This approach is not always effective, and by introducing a random pattern in the sorted output, makes errors harder to detect in the trayed output.
Mail once swept from the pockets must be transferred to trays for further processing. Such trays are arranged on racks with rows and columns of bins or compartments. A human worker takes the swept mail pieces and places them into a designated tray in an associated compartment. A full tray is then removed from the tray rack for further processing. In presently practiced sorting systems of this sort, no attention has been paid to improving the efficiency or ergonomics of this transfer operation, particularly for three-dimensional pocket arrays on single or multi-sided machines.
According to a first aspect of the invention, it is determined in advance for a given sort scheme or sub-scheme the number of mail pieces to be sorted to each pocket having an associated destination code or grouping of codes. Given this information, pockets are assigned associated destination codes in a manner which approximately equalizes the number of mail pieces to be sorted to each of a plurality of predetermined pocket array zones for which a single sweeper (human or robotic) is assigned. In this manner, the process ensures that no one zone will receive a disproportionate number of mail pieces, thereby improving overall efficiency and avoiding overloading a human worker. The robotic sweeper may become more efficient by optimizing its motions.
In one such process for sorting mail pieces, a sorting machine is used having a first array of pockets and a second array of pockets physically separate from the first array of pockets. The first and second arrays are swept of mail pieces by separate sweepers. The number of mail pieces sorted to each array are equalized in order to equalize the volume of mail pieces swept by each sweeper. In particular, where each pocket corresponds to a destination code and a total number of mail pieces per destination code is known in advance for each sort scheme to be carried out on the sorting machine, the equalizing step involves assigning destination codes to specific pockets to different sweeper zones in a manner that equalizes the volume of mail pieces swept by each sweeper, though the number of pockets/sweeper zone may not be equal.
According to a second aspect of the invention, the specific location of a pocket within each sweeper zone and the compartment for the corresponding tray on the storage rack are assigned based on ergonomic parameters. In particular, the system seeks to minimize the difference in vertical movement between the sorter pocket and its associated tray compartment for pockets for common destination codes. The number of physically cumbersome transfers (e.g., from a high pocket to low tray or a low pocket to a high tray) is kept at a minimum to increase speed and reduce fatigue. For robotic systems, the xe2x80x9cmasterxe2x80x9d process planner optimizes the xe2x80x9cslavexe2x80x9d robot by using array schemes to increase robot throughput by motion and time to sweep, based in part on robot characteristics.
In one process according to this second aspect of the invention, mail pieces are sorted to pockets in a vertically and horizontally extending array, wherein each pocket corresponds to one or more destination codes in a sort scheme. Mail is swept from the pockets to trays stored on a vertically and horizontally extending rack having rows and columns of bins containing trays. The number of mail pieces associated with each destination code in the sort scheme is determined, and destination codes are assigned to pockets and to trays at specific positions on the rack in a manner that minimizes the amount of vertical travel in sweeping sorted mail from the pockets and moving it to its designated tray. For purposes of the invention, it will be understood that the word xe2x80x9cminimizesxe2x80x9d is a relative term dependent on the degree of efficiency desired, and does not require total or absolute minimization. In a preferred embodiment, the rack is divided into a plurality of vertical tiers which receive mail from different sort schemes or sub-schemes, and destination codes are assigned to pockets and to trays at specific positions on the rack in a manner that minimizes the amount of sweeper travel, vertical or horizontal, in sweeping sorted mail from the pockets over all of the sort schemes. In another aspect of the invention, destination codes may be assigned to pockets and trays at specific positions on the rack in a manner that minimizes the amount of mail swept to trays in the highest and lowest rows of the rack.
The first and second aspects of the invention, especially when used in combination, greatly improve the ergonomics or robotic throughput of the sweeping operation. These and other features of the invention, including systems for carrying out the foregoing processes, are discussed in the detailed description which follows.
A third aspect of the present invention uses a priori or first pass data to create sort schemes which minimize the time items spend in the machine by creating pocket array zones which have zones near the input end of the machine receiving more volume than zones, for example, at the far end. Effective throughput is increased because high volume pockets at the near front end receive the most items, thus reducing the physical distance traveled in the sorter, minimizing the chance for jams or stoppages. Since higher volume sorts or destinations can exit the machine sooner, the mail items scheduled for secondary sorts can be recirculated to the feeder or transported to secondary sorting machines sooner, reducing dwell or delay time in a multiple machine plant in the latter case, and making possible for the first time plant optimization using this process improvement. This third aspect is also disclosed in the following.
All aspects apply to scheme development for not only a priori information but also secondary or tertiary sort schemes. Hence schemes and, consequently, overall system performance are optimized based on process analysis using first or primary pass derived information, or a priori information, or both.